Pressure fluid motor



Dec. 17, 1940. F. E. sxNcLAlR 2,224,862

PRESSURE FLUID MOTOR Filed March l, 1940 Patented Dec. 17, 1940 UNITED STATES PATENT OFFICE Sullivan Massachusetts Company, a corporation oi Application March 1, 1940, Serial No. 321,149 14 Claim. (CL 121-19) This invention relates to pressure iiuid motors, and more particularly to improvements inpressure fluid motors of the reciprocating piston, percussive type especially designed for use in hammer rock drills.

An object of this invention is to provide an improved pressure fiuid motor having improved iiuid distribution means. Another object is to provide an improved iiuid distributing valve mechanism for a pressure iiuid motor. A further object is to provide an improved pressure iluid motor o! the reciprocating piston, percussive type especially designed i'or use in hammer rock drills. A still further object is to provide an improved iluid distributing valve mechanism of the multi-valve type. Yet another object is to provide an improved valve mechanism embodying a pair of cooperating, relatively movable iiuid distributing valves and having embodied therein improved means for eilecting movement of the valves into their diiierent operating positions. These and other objects oi' the invention will, however, hereinafter more fully appear.

In the accompanying drawing there is shown for purposes of illustration one form which the invention may assume in practice.

In this drawing: 'i

Fig. 1 is a view in central longitudinal section taken through a pressure fluid motor constructed in accordance with an illustrative embodiment of the invention.

Figs. 2 and 3 are views similar to Fig. 1, showing the moving motor parts in diil'erent operating position.

Fig. 4 is an enlarged iragmentaryview taken on the plane oi Fig. l, showing a portion oi the improved valve mechanism.

In this illustrative embodiment of the invention the improved-pressure iluid motor is shown embodied in a hammer rock drill, although it will be evident that various features of the invention may be embodied in percussive tools of various other types. and in motors adapted for other uses.

'I'he pressure iiuid motor disclosed herein comprises a cylinder I having a bore 2 containing a reciprocatory hammer piston 3. The hammer piston has a piston head I slidingly fitting. the walls of the cylinder bore and a forwardly projecting striking bar 5 adapted to deliver impact blows to the shank of a usual drill steel. The cylinder has a front head 6 closing the front end of the cylinder bore. and the piston striking bar 55 is guided in a bore in this head. The rear end or the cylinder has an enlarged bore l arranged in axial alinement with the cylinder bore, and a rear cylinder head I closes the rear end of the cylinder bore and has a circular portion iltting the bore 1 and seated against a shoulder I at the 5 front end ot the bore 1 in the manner shown. Also arranged in the 'bore 'I is a rear member I0,

a ratchet ring Il and elements I2 and Il which cooperate with the rear cylinder head I to provide a valve chest. A rear head block Il suitlo ably secured to the motor cylinder engages the member i0 to hold the elements il, Il, i2 and Il in position against the rear cylinder head 8. The elements I, Il, Il, l2 and il are held against rotation within the bore l with respect to the 15 cylinder in any suitable manner.

As is usual in hammer rock drills. the drill steel is intermittently rotated as it is percussively actuated by the hammer piston, and the drill steel rotation means includes a rotatable pawl 20 carrier Il carrying usual spring-pressed pawls engageable with the ratchet teeth l of the ratchet ring Ii. The pawl carrier has integral therewith a spirally grooved `:fiile bar I'l which has a sliding interlocking connection with a riile nut il secured within the hammer piston. The riile bar has a rearward cylindric projection I9 liournaled in an axial bore in the rear member I0. The ratchet and pawl mechanism, together with the riile bar. serves to eiiect rotary movement of the hammer piston as the latter moves rearwardly during its return stroke, and the rotary piston motion is transmitted tothe drill steel through straight grooves 2l on the piston striking bar I which cooperate with a usual chuck nut secured to the drill steel chuck in the manner well understood by those skilled in the art. It will thus be seen that when the hammer piston reciprocates to ei'i'ect percussi" actuation of the drill steel, the latter is interm. .ently rotated.

The i'iuid distribution valve mechanism may be generally similar to that disclosed in the cepending applications to John C. Curtis. Ser. No. 152,609, iiled July 8, 1937, and Ser. No. 315,786, filed January 26, 1940, and the present invention constitutes an improvement over the subject matter disclosed in these applications. The element il of the valve chest has alined end bores 2i, 2| spaced by an inwardly directed annular partition 22 bounding a reduced bore 23 interconnect- 50 ing the alined end bores. The bores 2|, 23 receive a pair oi' cooperating, relatively movable, tiuid distributing valves 24 and 2B. These valves are movable into abutting relation and havev sleeve-like bodies arranged in telescopic sliding exterior periphery of the larger sleeve-like body of the front valve 24 slidingly ts the bore 23 in the partition, and the exterior periphery of the smaller sleeve-like body of the valve 25 slidingly ts the bore in the larger sleeve-like valve body, as clearly shown in Fig. 4. Extending inwardly from the sleeve-like bodies of the valves are internal annular flanges 28 and 26. The rear cylinder head 8 has a sleeve portion 30 extending rearwardly through the valves, and the element I2 has an axial bore within which the rear end of this sleeve portion is tightly fitted. In this instance, the rifle bar I1 is journalled in and extends axially through the bore in the sleeve portion. 29 cooperate respectively with a cylindric projection 3I formed on the exterior of the sleeve portion 30 and a cylindrlc projection 32 formed on the valve chest element I2, thereby to provide restricted annular spaces 33 and v34 for metering the flow of pressure fluid from a supply chamber 35 within the valves past the valves to the opposite ends of the cylinder bore. Formed in the front face of the valve chest element I2 is an annular recess 36 connected by a port 31 with a distributing passage 38, the latter in turn being connected by a port 39 with the front end of the cylinder bore. Distribution passages 40 in the rear cylinder head 8 connect the front end bore 2I at the front side of the front valve 24 directly with the rear end of the cylinder bore.

The means for supplying pressure fluid to the supply chamber 35 within the valves comprises a throttle valve 43 arranged in a transverse bore in the rear head block I4 and having an internal fluid supply chamber connected by a port 44 with a passage 45 in turn communicating with a chamber 46 in the member III. Pressure fluid may be conducted from the chamber 46 through a passage 41 and through the ratchet ring II, through the spaces between the pawl carrier and pawls and the ratchet teeth' I6 to a passage 46 communicating with an annular recess 43 in the element I2, thisrecess in turn connected with an annular passage 56 surrounding the sleeve portion 30 and formed within the cylindric projection 32. The passage 58 communicates directly with the fluid supply chamber 35 within the valves. A throwing passage I communicates through a port 52 with the front end bore 2| at the rear side of the front ,valve flange 26, and this throwing passage is connected by a port 53 with the cylinder bore. An annular exhaust groove 54 is formed in the walls of the cylinder bore substantially midway between the ends thereof and is connected directly to atmosphere throughout an exhaust port 55. The port 52 is connected to a restricted vent port 56 through passages 51 and 58 formed in the Lelements I2 and I3 respectively. A recess 53 c ommunicates with the distribution passage 38, and a restricted passage 66 connects this recess with the rear end bore 2l at the front side of the external flange 21 of the rear valve 25.1 restricted leak passage 6I connects the fluid supply chamber 35 with the rear end of the cylinder bore. Pressure fluid owing through the port 68 to the front end of the rear end bore 2l at the forward side of the external flange 21 of the rear valve 25 acts on the front pressure area of the external ange so that the opposing pressures on the equal pressure areas at the opposite sides of the external ange are balanced.

The internal valve flanges 28 and The mode of operation of the improved pressure fluid motor .is as follows. When the parts are in the position shown in Fig. 1, pressure uid may flow from the throttle valve 43 through port 44, passage 45, chamber 46, through the spaces surrounded by the ratchet teeth I6 of the ratchet ring, and thence through passage 48, recess 46 and annular passage 56 to the uid supply chamber 35 within the valves 24 and 25. Pressure fluid may then flow from the supply chamber 35 through the restricted annular space 33, through the front end bore 2I past the front face of the front valve 24, and through distribution passages 40 to the rear end of the cylinder bore at the Vrear side of the piston head of the motor piston. Concurrently, the front end of the cylinder bore and the end bore 2| at the opposite sides of the external flange 21 of the rear valve 25 are connected to exhaust through the exhaust groove 54. The pressure fluid flowing past the front face of the front valve 24 holds the latter in its rearmost open position with its rear end in abutting engagement with the rear valve 25 and thereby maintains the-rear valve in its closed position. Pressure uid flowing through the passages 40 to the rear end of the cylinder bore acts on the rear pressure area of the piston head to move the motor piston forwardly to effect its working stroke. As the motor piston moves forwardly from the position shown in Fig. 1, the leading edge of the piston head first overruns the port 53 and thereafter overruns the exhaust groove 54, and upon continued forward piston movement the following edge of the piston head uncovers the port 53 of the throwing passage 5I, admitting pressure fluid from the rear end of the cylinder bore through port 53, passage 5I and port 52 to the rear end of the front bore 2| at the rear side of the external flange 26 of the front valve 24; and as a result the pressure fluid acts on the eil'ective pressure area of the valve flange to throw immediately the front valve forwardly from the position shown in Fig. 1 to its position shown in Fig. 2. The pressure of the fluid acting on the inner surface of the internal flange 23 of the front valve 24 is somewhat higher than the opposing pressure acting on the outer surface of the flange, due to the restriction at 33, and this higher pressure aids in the throwing of the valve. When the front valve 24 is in its foremost position, it is seated at its front end against the rear face of the rear cylinder head 8 while the rear valve 25 is still momentarily maintained in its rearmost closed position. Accordingly, when the valves are in the position shown in Fig. 2, flow of pressure fluid to the cylinder bore is momentarily completely cut off. and as the motor piston continues to move forwardly by expansion of the duid and momentum, pressure fluid trapped in the front end of the cylinder bore will be compressed. This compression pressure acts through passage 33 on the effective rear pressure area of the external flange-21 of the rear valve 25, and since the pressure acting on this areawlli, due to the restricted port 66, build up more rapidly than that acting on the opposing area, the valve 25 will be seasonably thrown forwardly from the position shown in Fig. 2 to its open position shown in Fig. 3. When this valve is thrown forward (opened) it will be held open by the action of live fluid on its full. rearwardly facing area. It will be noted that as the motor piston completes its forward movement, its folmotor operation, and power to keep the motor lowing edge uncovers the exhaust groove Il to connect the rear end of the cylinder bore and the front end of the front end bore 2i at the iront side of the front valve 24 to exhaust. The motor piston will continue, however, to move forwardly by momentumv and will deliver its blow to the drill steel shank. .The pressure luid flowing past the rear face of the rear valve 2l, as noted above, holds the latter in its foremost open position, and since its forward end will be in abutting engagement with the front valve, it will thereby maintain the front valve in its closed` position. When the rear valve 2l is in the position shown in Fig. 3, pressure fluid will iiow from the supply chamber 3l,through the restricted clearance space ll, past the rear face of the rear valve 2l and through port 31. distribution passage Il and port 2O to the front end oi the cylinder bore at the front side oi the piston head of the motor piston. the pressure iiuid acting on the front pressure area of the piston head to move the piston rearwardly to eilect its return stroke. As the motor piston moves rearwardly from the position shown in Fig. 3, the pressure iiuid in the front end of the cylinder bore expands due to piston movement, so that the pressure in the front end of the cylinder bore and in the distribution passage 22, port 31 and recess 38 is substantially lower than that in the supply chamber and as a result the pressure acting on the inner pressure area of the internal flange 29 and the forward end of the valve body, which pressure is substantially higher than that acting on the rear face of the valve due to the restriction at Il, acts on the rear valve to throw the same, at an appropriate time, rearwardly from the position shown in Fig. 3 to its position shown in Fig. 2. Due to the restricted passage 80, it will be appreciated, the pressure in the front end of the rear end bore 2i at the front sidev of theexternal ange of the rear valve will remain substantially higher than the pressure in the" distribution passage 3l as the latter pressure falls upon rearward piston movement, and this somewhat higher pressure aids in the rearward throwing of the rear valve. It may be noted, with reference to the restricted passage 80, that its size is of substantial importance since its delaying of the building up of pressure within the space with which it communicates insures rear valve opening, and its retardation of pressure drop in that space is important in determining the time of reary 'and momentum, the leading edge of the piston head overnms the port 53, and the following edge of the piston head thereafter uncovers the exhaust groove, thereby connecting the front end of the cylinder bore and the rear pressure area of the rear valve to exhaust. It will be evident that the further reduction in pressure in the forward end of the cylinder and in the passage 38 would then, were it not already closed, substantially instantly close the rear valve 25. 'I'his is important, for, while during normal drilling closure of the rear valve will precede uncovering of the exhaust by. the front end of the piston head, when the drilling is very heavy due to resistance to rotation, and so rearward piston` movement may be slowed down, with diminished pressure drop during the rst half or so of rearward piston travel, so that rear valve closure by such a pressure drop may not take place, valve lshifting on exhaust opening will still insure moingwiilbeassuredbythedelayincut-oi! for the front end. Upon eontinued'rearward piston movement by momentum, the pressure fluid trapped in the rear end of the cylinder bore is compressed, and this compression pressure acts on the eifective front pressure area of the ex-` ternal flange 2i ofthe front valve to throw the latter rearwardly to its initial position shown in Fig. 1. The sequence of operations above described will be rapidly repeated during normal running of the motor.

The restricted vent passages Si, il and Il and the restricted leak passage Il have no material effect during the normal operation of the motor. However, if the piston should stall in its rearward position in the rear end of the cylinder bore, the pressure fluid leaking through the passage li will build up in the rear end of the cylinder bore sumciently to effect forward piston movement, thereby to effect starting of the motor. When the motor is under substantial load, for instance when the resistance to drill steel rotation becomes abnormally high, the rearward stroke of the motor piston may be shortened, but reclprocation of the piston will still occur, since when the piston head covers the port 53, though it may not move rearward far enough to vent passage BI, still the pressure in the bore 2i at the rear side of the external iiange 2t of the front valve 24 will leak to atmosphere through the vent passages, and so the compression pressure built up by the piston head as the rear end of the piston continues to move rearwardly beyond the port 53, will act on the front face of the front valve to throw the latter rearwardly into its open position.. Pressure iluid may then ilow'to the rear end of the cylinder to drive the piston forwardly. It will thus be seen that starting of the motor when stalled is assured and reclprocation of the piston will occur even when the resistance to drill steel rotation becomes abnormally high, though with shortened strokes, thereby preventing stopping of the motor during overload under certain conditions.

As a result of this invention an improved pressure iiuid motor is provided having improved iluid distributing valve mechanism. It will further be evident that by the provision of a fluid distributing valve mechanism of the multi-valve type, together with the improved means for effecting movement of the valves into their different operating positions, the structure of the motor is not only simplified but also operating eiliciency is increased. Other uses and advantages of the improved pressure iluid motor will be clearly apparent to those skilled in the art.

While there is in this application specically described one form which the invention may assume in practice, it will be understood that this form of the same is shown for purposes of illustration and that the invention may be modifled and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In a pressure fluid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said bore, a piston-controlled exhaust for said cylinder bore, a iiuid supply, and means for distributing pressure fluid to effect reciprocation of said piston including a. valve chest having a valve chamber, a fluid distributing valve in said valve chamber, a iiuld distribution passage leading from said valve chamber to said cylinder bore, said valve controlling the communication of said distribution passage with said fluid supply, and means for subjecting said valve to valve throwing pressures for moving said valve into its different operating positions including opposed equal pressure areas on said valve subjected to the pressure in said distribution passage, the communication of both of said areas with said distribution passage being with the latter at points therein short of the cylinder bore and the communication of one of said pressure areas with said` distribution passage being relatively rest'ricted 2. In a pressure iiuid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said bore, a .piston-controlled exhaust for said cylinder bore, a fluid supply, and valve means including a valve chest having a valve chamber, a fluid distributing valve in said valve chamber, a fluid distribution passage leading from said valve chamber to said cylinder bore, said valve controlling the communication of said distribution passage with said fluid supply, and means for subjecting said valve to valve throwing pressures for moving said valve into its different operating positions including opposed equal pressure areas 4on said valve subjected to the pressure ln said distribution passage, the communication oi one of said pressure areas with said distribution passage being relatively restricted, and at a point short of the cylinder bore end of said distribution passage, and a pressure area on said valve subjected to the pressure in said fluid supply.

3. In a pressure fluid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said bore, a piston-controlled exhaust for said cylinder bore, a uid supply, and

40 valve means including a valve chest having a valve chamber, a fluid distributing valve in said valve chamber, a iiuid distribution passage leading from said valve chamber to said cylinder bore, said valve controlling the communication of said 45 distribution passage with said fluid supply, and

means for subjecting said valve to valve throwing pressures for moving said valve into its diierent operating positions including opposed equal pressure areas on said valve subjected to the pressure 50 in said distribution passage, the communication of both of said pressures areas with said distribution passage being independent of the cylinder bore and the communication of one of said pressure areas with said distribution passage being relatively restricted, and additional opposed pressure areas on said valve respectively subjected to the pressure of said uid supply and to the pressure in said distribution passage.

4. In a pressure iiuid motor, the combination comprising a, cylinder having a bore, a piston reciprocable in said bore, a piston-controlled exhaust for said cylinder bore, a iiuid supply, and valve means including a valve chest having a valve chamber, a fluid distributing valve in said 5 valve chamber, a fluid distribution passage leadbore and the communication of one of said pressure areas with said distribution passage being relatively restricted, additional opposed pressure areas on said valve respectively subjected to the pressure in the fluid supply and to the pressure in said distribution passage, and means providing a restricted communication between said last mentioned opposed pressure areas.

5. In a pressure fluid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said cylinder bore, a piston-controlled exhaust for said cylinder bore, a fluid supply, a valve chest having a valve chamber, uid distribution passages leading from said valve chamber to the opposite ends of said cylinder bore, relatively movable iiuid distributing valves in said valve chamber for respectively controlling communication of said distribution passages with said iiuid supply, and means for subjecting said valves to valve throwing pressures for moving said valves into their different operating positions including opposed pressure areas on said valves adapted to be subjected to valve throwingpressures, one of said valves having equal opposed pressure areas constantly subjected to the pressure in the iluid distribution passage controlled thereby, the communication of one of said equal opposed pressure areas with said distribution passage being relatively restricted.

6. In a pressurev fluid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said cylinder bore, a piston-controlled exhaust for said cylinder bore, a iiuid supply, a valve chest having a valve chamber, fluid distribution passages leading from said valve chamber to the opposite ends of said cylinder bore, relatively movable fluid distributing valves in said valve chamber for respectively controlling communication of said distribution passages with said fluid supply, and means for subjecting said valves to valve throwing pressures for moving said valves into their different operating positions including opposed pressure areas on said valves adapted to be subjected to Valve throwing pressures, one of said valves having equal opposed pressure areas constantly subjected to the pressure in the fluid distribution passage controlled thereby, the communication of one of said equal opposed pressure areas with said distribution passage being relatively restricted, and other opposed pressure areas on said latter valve, one constantly subjected to the pressure in the fluid supply and the other communicable with said latter y distribution passage.

7. In a pressure fluid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said cylinder bore, a piston-controlled exhaust for said cylinder bore, a fluid supply, a valve chest having a valve chamber, uid distribution passages leading from said valve chamber to the opposite ends of said cylinder bore, relatively movable fiuid distributing valves in said valve chamber for respectively controlling communication of said distribution passages with said fluid supply, and means for subjecting said valves to valve throwing pressures for moving said valves into their different operating positions including opposed pressure areas on said valves adapted to be subjected to valve throwing pressures, one of said valves having equal opposed pressure areas constantly subjected to the pressure in the fluid distribution passage controlled thereby, the communication of one of said equal opposed pressure areas with said distribution passage being relatively restricted, other opposed pressure areas on said latter valve, one constantly subjected to the pressure in the iluid sup-- ply and the other communicable with said latter distribution passage, and means providing arein said valve chamber for respectively controlling communication of said distribution passages with said iluid Supply. and means for subjecting said valves to valve throwing pressures for Imoving said valves into their di'erent operating positions including opposed pressure areas von said valves adapted to be subjected to valve throwing pressures, one of said valves having equal opposed pressure areas constantly subjected to the pressure in the uid distribution passage controlled thereby and further having other opposed pressure areas, one constantly subjected to the pressure in the iluid supply and the other communicable with said latter distribution passage, the communication of 4one of said equal opposed pressure areas with said distribution passage being relatively restricted, whereby a drop in pressure in said last mentioned distribution passage, due to expansion of uid, causes the pressure within said iuid supply acting on said pressure area subjected to the pressure in said uid supply to effect throwing of said valve.

9. In a pressure iiuid motor, the combination comprising a cylinderhaving a bore, a piston-reciprocable in said cylinder bore, and uid distribution means for said cylinder including a valve chest having a valve chamber, a pressure fluid supply, a pair of cooperating, relatively movable,

fluid distributing valves in said valve chamber, distribution passages leading fromv the opposite ends of said valve chamber respectively to the opposite ends of said cylinder bore, said valves respectively controlling communication of said distribution passages with said iluid supply, and means for subjecting said valves to valve throwing pressures for moving said valves into their different operating positions including pressure areas on said valves subjected to the pressure in said iuid supply and opposed pressure areas subjected to the pressure in said distribution passages, meansV on said valves cooperating with elements of said valve chest for providing restricted communication between said fluid supply and said distribution passages, a passage communicating with the cylinder bore and controlled by said piston for subjecting a pressure area on one of said valves to a valve throwing pressure, and a passage for connecting' said uid distribution passage controlled by said other valve with a pressure area on said latter valve, independently of the cylinder bore, so that opposed equal pressure areas on said latter valve are balanced.

10. In a pressure uid motor, the combination comprising a cylinder having a bore, a piston reciprocable in said cylinder bore, and fluid distribution means for said cylinder including a valve chest having a valve chamber, a pressure fluid supply, a pair of cooperating, relatively movable, fluid distributing valves in said valve chamber, distribution passages leading from the opposite ends of said valve chamber respectively to the opposite lends of said cylinder bore, said valves respectively controlling communication of said distribution passages with said uid supply, and means for' subjecting said valves to valve throwing pressures for moving said' valves into their diii'erent operating positions including pressure areas on said valves subjected to the pressure in vsaid fluid supply and opposed pressure areas subjected to thepressure in said distribution passages, means on said valves cooperating with elements of said' valve chest for providing lrestricted communication between saidl fluid supply and said distribution passages, a passage communicating wit h the cylinder bore and controlled by said piston for subjecting a pressure area on one of said valves to a valve throwing `\p`ressure, apass'age for connecting said uid distribution. passage controlled by said other valve with a pressure area on said latter valve so that opposed equal pressure areas on said latter valve are balanced, and vent passage means for providing a continuous restricted vent between said second mentioned passage and the atmosphere..

1l. In a pressure iiuid motor, the combination -of a cylinder having a bore, a piston reciprocable in said cylinder bore, a piston-controlled exhaust for said cylinder bore, a fluid supply, and'valve means including a valve chest having a valve chamber, a fluid distributing valve in said valve chamber, a fluid distribution passage leading from `said valve chamber to vsaid cylinder bore, said valve controlling communication of said distribution passage. with said fluid supply, and means for subjecting said valve to valve throwing pressures for moving said valve into its different operating positions including opposed equal pressure areas on said valve, one of said pressure'areas communicating directly with said distribution passage, and a restricted passage connecting said` other pressure area with said distribution passage at a point short of the latters communication with the cylinder bore. A

12. In a pressure iluid motor, the combination of a cylinder having a bore, a piston reciprocable in said cylinder bore, a piston-controlled exhaust for said cylinder bore, a iiuid supply, and valve means including a valve chest having a valve chamber, a iluid distributing valve in said valve chamber, a uid distribution passage leading from said valve chamber to said cylinder bore, said valve controlling' communication of said distribution passage with said iluid supply, and means for subjecting said valve to valve throwing pressures for moving said valve into its different operating positions includingopposed equal pressure areas on said valve, one of said pressure areas communicating directly with said distribution passage, a restricted passage connecting said other pressure area with said distribution passage independently of the cylinder bore, and additional' opposed pressure areas on said valve respectively subjected to the pressure of said fluid supply and to the pressure in said distribution passage.

13. In a pressure tluid motor, the combination of a cylinder having a bore, a piston reciprocable in said cylinder bore, a piston-controlled exhaust for said cylinder bore, a fluid supply, and valve means including a valve chest having a valve subjecting said valve to valve throwing pressures Ir moving said valve into its dierent operating positions including opposed equal pressure areas on said valve, one of said pressure areas communicating directly with said distribution passage, a restricted passage connecting said other pressure area with said distribution passage independently oi the cylinder bore, additional opposed pressure areas on said valve respectively subjected 'to the pressure of said nuid supply and to the pressure in said distribution passage, and means providing a restricted communication between said last mentioned pressure areas whereby the now of pressure iluid from said iluid supply to said distribution passage is restricted.

14. In a pressure iiuid motor, the combination of a cylinder having a bore. a piston reciprocabie in said cylinder bore, a piston controlled exhaust for said cylinder bore. and motive iluid distribution means for said cylinder including a valve, a iluid conducting passage leading to one end oi' the cylinder bore, and means for eecting valve 5 throwing to interrupt supply to said passage when the piston uncovers said exhaust during heavy drilling and earlier during normal drilling including means for creating an eective valve throwing dinerential pressure prior to release for said cylin- 10 der end during normal motor operation. said last mentioned means including passage means for connecting an area. on said valve with said fluid conducting passage, said passage means opening into said iluid conducting passage at a point be- 1li tween the ends oi the latter.

FRANK E. SINCLAIR. 

